200 have been killed after heavy rain caused a severe mudslide in the west african nation of sierra l leone. [car horns honking] [insects chirping] amarasekaren: oo oo oo! what's happening? what's happening? no big problem, huh? ok. whenen we get probm... man: whoa!! [men shouting] [indistinct conversation] narrator: while freetown residents fight for acccountability, in san francisco, climate change isn't debabated as mucuch as it's mitigateded. billions of dollars are pouring into the bay area, but is tech-driven development prepared for a sea level that's rising? scholl: san francisco is experiencing a tremendous building boom and has been for the last 5 years. tam: we have ucsf hospital. we have the warriors coming. we have a bunch of new apartment buildings. scholl: you have corporate headquarters of facebook, google, microsoft. christensen: we realize we live in such an amazing place with so much creativity and innovation. i'm excited when i see the young people in the tech industry all overer town, allll over the e by area commuting backck and forth. there's an energy here. renteria: